The use of fluids to treat subterranean formations penetrated by a well bore containing hydrocarbons to increase the permeability, conductivity and production from these formations is well known in the art. The process of treating the formations to increase conductivity through the use of these fluids is known as "fracturing" the formation. Generally, in a fracturing process, a fluid of sufficient viscosity is pumped and/or injected into the formation at sufficient pressure and rate to fracture the formation. The fracturing fluid is of sufficient viscosity to carry proppant into the formation and of sufficient viscosity to obtain fracturing of the formation at high pressure, shear and temperature. The proppant consists of such materials as sand, glass beads, sintered bauxite, fine gravel and the like. The proppant is carried into the fracture and helps keep the formed fractures open after fluid recovery. The newly formed fracture is held open by proppant which provides increased routes or channels through which hydrocarbons can flow increasing production. Various fracturing fluids and processes for their use are known in the art. The art discloses the use of slurries, emulsions and gels. More recently, it was discovered that foams could be used in place of the known slurries, emulsions and gels. See U.S. Pat. No. 3,937,283 to Blauer.
As described in Blauer, various gases and liquids can be used to compose the fracturing foam. Generally, the foams include nitrogen, carbon dioxide and water with a suitable surfactant. The foam, as with the slurries, gels and emulsions in the art, containing proppant is pumped into the formation at such a pressure that it causes the fracture of the formation. However, unlike the previous fracturing systems, the use of foams increases well clean up due to the fact that the foam is easily removed from the well because when the pressure is released or reduced, the foam expands. Various foam fracturing systems are known in the art.
Generally, in making a foam, a fracturing gel is first made from water or brine, a gelling agent, i.e., a polymer and a suitable surfactant. The water or brine may contain up to about 20% alcohol, for instance, methanol. In addition, the fracturing gel may be crosslinked by use of known crosslinkers. After the gel is made, a foamer is added and the gel with the roamer is added to an energizing phase such as carbon dioxide or nitrogen or a combination of carbon dioxide and nitrogen to create a foam. Various systems for the addition of the energizing phase to the gel phase have been described in the art. Indeed, various systems have been devised wherein the carbon dioxide is added as the gel is pumped down hole into the well bore and subsequently into the formation.
Various foamers are known in the prior art. For example, see U.S. Pat. Nos. 4,480,696, and RE 32,302. Betaines are known roamers. Betaines are multipurpose foaming agents or foamers primarily used in foam fracturing applications. Betaines are used to foam aqueous fluids while offering excellent detergency and interfacial tension-reducing properties. Betaines are particularly applicable to any reservoir which is generally classified as "water sensitive," that is, a reservoir which is slow to return water-based treatment fluids. Such reservoirs are often characterized by low permeability, and moderate amounts of clay or shale. Betaines offer superior performance in high temperature wells, where other foamers degrade.
Originally, fracturing foams were made utilizing a dry polymer which was mixed with water and the foamer before addition of the energizing phase. However, the use of a dry polymer, i.e., gelling agent was not conducive to fracturing systems wherein the water was gelled as it was pumped, that is, dry polymer was more limited to first mixing the polymer with water until a gel was formed and then pumping the gel for addition with the energizing phase and subsequent introduction into the formation. This method required more energy to be supplied by the surface pumps due to the increased viscosity of the gel. Further, if the fracturing job using the dry polymer system had to be abandoned or terminated permanently, the disposal of the pre-mixed gel created a problem.
In response to the above problems, a slurried polymer system was introduced into the market by The Western Company of North America. Western's slurried polymer system utilizes 50% diesel oil and 504 of a guar or guar-based polymer. The slurried polymer system of Western can include other liquid hydrocarbons besides diesel oil; for example, kerosene, naphtha, light mineral oil, and the like. Further, the fracturing gel made utilizing the slurried polymer system can be crosslinked. This system provides the advantage of being able to supply the gelling agent polymer in liquid form to the aqueous fluid as the aqueous fluid is pumped into the formation. If the fracturing Job has to be discontinued, then the supply of polymer is simply stopped, thus, the user does not have to face disposal problems of unused gel. Further, there is provided a system which increases in viscosity while being pumped, decreasing surface pump horsepower needed. However, it was discovered that the slurried polymer system was not compatible with fracturing gels utilizing an alkylbetaine, i.e., cocobetaine, as the foamer. It was specifically discovered that diesel oil and other liquid hydrocarbons used in the system are very efficient defoamers and made the use of the slurried polymer system with the betaine foamer undesirable due to the lack of stability of the foam produced.
Therefore, a need exists for a foamer which is compatible with the slurried polymer system utilizing a liquid hydrocarbon like diesel oil and demulsifiers as components. The present invention provides foamers which are compatible with a slurried polymer system and provides a foam which has the desired theological properties under high temperature, shear and pressure.